The present invention relates to an apparatus and a method for forming a flexible circuit of predetermined design, and in particular to the making of a functioning flexible circuit by depositing multiple layers of a variety of materials in a predetermined configuration onto a substrate.
A number of methods and techniques for making circuit boards of a predetermined design are known. In accordance with conventional techniques, the desired circuit is initially drawn, either manually or automatically utilizing a computer-aided design program. The prototype circuit is ultimately assembled in the desired configuration through the use of a variety of pre-prepared electronic components and a manual assembly process onto a rigid or flexible base having a pattern of metal conductor traces defining the circuit. The circuit may ultimately be assembled semi-automatically, provided sufficient automation equipment is available and can be justified.
Circuit boards typically include a plurality of individual active and/or passive components that are fastened to a surface of the board, and interconnected using metal conductive traces on an insulating substrate. While early circuit boards used insulating layers made of a rigid fiberglass-reinforced resin or ceramic material, many printed circuit boards in use today employ flexible substrates, typically made of a polyester or polyimide material. As electronic systems required greater speed and complexity in smaller packages, printed circuit designers have developed printed circuit boards having smaller and shorter traces to achieve greater circuit densities.
Although they are called xe2x80x9cprinted circuits,xe2x80x9d such circuit boards are typically formed using plating, lithography, and etching technologies. For example, one or both of the opposing surfaces of an insulating substrate are completely covered with a conductive metal such as copper, using methods such as electroless and electrolytic plating. A photoresist layer is deposited over the conductive metal platings and exposed to a light or other radiation image of the desired circuit pattern. The unexposed photoresist is removed, and the uncovered portion of the conductive metal is etched away to reveal the desired conductive circuit patterns. Such photolithographic methods well understood, and are suited for certain high-volume production, but involve numerous steps.
Single-sided-single-layer circuits are the easiest to make, but often have unacceptably long conductive traces (thus having resistance and/or capacitance that is too high). Double-sided circuit boards increase wiring densities by providing two circuit layers fabricated on opposing sides of an insulating substrate. The two circuit layers are interconnected by conductors (typically, plated-through holes) that pass through the insulating layer. Multi-layer printed circuit boards have even higher densities, using two or more laminated and interconnected layers. However, unique problems exist in the fabrication of laminated multilayer printed circuit boards, such as properly sizing and aligning all of the interconnected layers for lamination.
Integrated circuit chips have been attached using surface-mount methods, typically by wave soldering or solder reflow. Methods and techniques for making three-dimensional articles of a predetermined size and shape are also known. U.S. Pat. No. 5,121,329 issued to S. Scott Crump discloses apparatus and a process for forming a three-dimensional (3D) object of predetermined design, in particular to the making of a model or article by depositing multiple layers of a material in a fluid state onto a base. The material is selected and its temperature is controlled so that it solidifies substantially instantaneously upon extrusion or dispensing onto a base, with the build-up of the multiple layers forming the desired article. For example, the object can be modeled and designed in a computer, and then a 3D prototype of the object could be built by extruding fluid plastic onto a base according to instructions from the computer. However, no description of building electronic circuits is provided in this reference.
Thus, a need continues to exist for a relatively simple and efficient process and apparatus by which designers may design and create circuits, particularly flexible circuits, in an automated process. The process and apparatus disclosed herein meets that need with the same ease and simplicity of using a desktop computer and printer, with the entire modeling process being carried out at the operator""s computer-aided design (CAD) work station.
The invention teaches a method and apparatus for forming a flexible circuit of predetermined design, and in particular to the making of a functioning flexible circuit by depositing multiple layers of a variety of materials in fluid or component form in a set configuration onto a substrate. A source for each of the materials is provided. In one embodiment, the materials are applied to the substrate through accurate positioning and moving of the dispensing heads in three dimensions and through accurate control of the amount of material applied.
In some embodiments, successive layers of electronic circuitry are formed by successively printing and then curing each layer, one on top of the last, starting with a flexible substrate, such as polyester film. Not only are conductive traces (i.e., wiring) printed (i.e., by dispensing and curing properly selected fluids) using the methods and/or systems described below, but also passive components (such as, for example, resistors, capacitors, and/or inductors), and/or active components (such as, for example, transistors, switches, amplifiers, filters, electric batteries, memory and/or logic).
Another aspect of the invention is to control the viscosity of the fluid within the source in order to control the flow characteristics of the fluid.
Yet another aspect of the invention is to control the temperature throughout the dispensing path in order to maintain accurate control of the flow characteristics of the fluid.
Yet another aspect of the invention is to provide accurate control of the velocity of the dispensing nozzles in order to control the volume of fluid per unit of base area.
Yet another aspect of the invention is to provide a means to cure the deposited materials at controllable time intervals during the process of forming the flexible circuit.